Electrothermal atomic-absorption spectroscopy was employed for measuring manganese in beta-cell-rich pancreatic islets microdissected from ob/ob mice. The islet content of endogenous manganese was 80 mumol/kg dry wt., which is about half as much as found in the exocrine pancreas. The initial uptake was characterized by two components, with approximate Km values of 35 microM and 3.7 microM respectively. After 60 min of incubation with 0.25 mM-Mn2+, the intracellular concentration of manganese ...